The invention relates to a method for actuating a hydraulic consumer and a hydraulic control system for supplying pressure medium to the consumer.
U.S. Pat. No. 5,138,883 A has disclosed a hydraulic control system in which a consumer such as a differential cylinder can be supplied via a valve device—which is equipped with two continuously adjustable directional control valves—with pressure fluid that is furnished by a pump. The supply to the consumer and the return from it each contain a respective continuously adjustable directional control valve. In their neutral positions, the directional control valves are prestressed into a closed position and, by means of pressure reduction valves, can each be moved in one direction in which the pump is connected to the associated pressure chamber and in another direction in which the respective associated pressure chamber is connected to the tank. In this known control system, through suitable triggering of the two directional control valves, the consumer can be operated with a so-called regeneration circuit. For example, when a cylinder travels outward, the contracting annular chamber is connected via the associated directional control valve to the pressure fluid inlet of the expanding annular chamber so that the cylinder is extended in a rapid movement. A disadvantage of the regeneration/differential circuit, however, is that due to the restraining of the consumer (effective area corresponds approximately to the piston rod area), the consumer cannot be operated with the maximum output.
If a control system of this kind is used in a mobile piece of equipment such as a backhoe loader, a mini- or compact excavator, or a telehandler, then the available digging power in the regeneration mode is too low due to the restraining of the consumer. Preferably, the regeneration mode is correspondingly used when lowering the machine component of the mobile piece of equipment. In order to operate the consumer with a high power, for example when digging or when lifting a load, a switch into the normal mode is executed, in which the expanding pressure chamber is connected to the pump and the contracting pressure chamber is connected to the tank.
In order to prevent the occurrence of cavitation in the pressure fluid supply with a pulling load, a load lowering valve can be provided in the return from the consumer, as is known, for example, from DE 196 08 801 C2 or from the data sheet VPSO-SEC-42; 04.52.12-X-99-Z from the company Oil Control, a subsidiary of the applicant.
The directional control valves are moved by means of a piloting device, which is equipped with pressure reduction valves and is actuated by a joystick; the operator decides when to switch from regeneration mode into normal mode.
In this case, it is often difficult to determine the correct moment to make the switch, as a result of which the consumer remains too long in the regeneration mode with reduced power or the switch to the normal mode is made prematurely even though it would be advantageous to operate the consumer at a high speed.
By contrast, the object underlying the present invention is to optimize the switching from regeneration mode to normal mode with regard to the energy savings entailed by the regeneration mode and the power available at the consumer.